Bipolar disorder is a dynamic illness with constantly changing symptom and syndrome presentations that confound interpretation of neuroimaging findings, as well as treatment response. This feature of the illness raises the need to examine patients as the condition evolves over time in order to clarify interactions between neuroimaging measures, clinical response and affective state. Careful longitudinal assessments and subject retention are critical elements to the success of the BITREC and its proposed projects. The Longitudinal Assessment Core (LAC) will serve this need and is a direct extension of over a decade of experience following young bipolar patients. Specifically, our experience with longitudinal studies is demonstrated by the success of a number of large, long-term projects. Our previous and ongoing projects provide an infrastructure for the longitudinal study of bipolar disorder from which the LAC will be developed. The LAC will be fully integrated with the other BITREC cores and projects as described in the Operational Plan. Dr. Paul Keck, Professor of Psychiatry and Pharmacology and Vice-Chair for Research in the Department of Psychiatry will direct the LAC. He will be responsible for overall core function and for overseeing infrastructure development. He will be assisted by several clinicians and staff to provide excellent clinical care and ongoing assessments to subjects enrolled in the BITREC. The LAC will hold staff meetings every other week to ensure that recruitment benchmarks are being met and to review subjects who have developed new affective episodes or symptoms in order to determine whether they qualify for additional BITREC projects. Standard operating procedures will be developed to maximize efficiency and meet objectives and benchmarks. Most decisions involving daily core function will be made by the personnel of the core under the direction of Dr. Keck. These decisions will be guided by and reported to the BITREC Steering Committee. Additionally, Dr. Keck will be integrated within the overall administrative structure of the BITREC by serving on the Steering Committee. With this structure established the LAC will be able to meet its primary functions which are: 1) to provide treatment to subjects actively participating in BITREC projects; 2) to provide ongoing clinical evaluations and excellent clinical care to subjects enrolled in the BITREC between projects;and 3) to identify subjects who meet criteria for a new BITREC project. By following and managing subjects across project, the LAC helps to further integrate the various components of the BITREC, assuring a cohesive and effective research center.